Polymers have proven to be some of the most difficult organic materials to stabilize against deleterious effects of oxygen and ozone, particularly unsaturated polymers, both natural and synthetic. Although many materials have been suggested and used as polymer stabilizers no completely satisfactory material has been found that will fully protect these polymers under the widely different conditions to which they are subjected.
Phenolic compounds have been among the more commonly used compounds that have found wide scale acceptance as polymer stabilizers. But many of the phenolic antioxidants, although reasonably effective stabilizers for organic materials, tend to impart discoloration and staining to the materials they are intended to stabilize.
In addition, some previously known phenolic antioxidants have limited solubility which causes difficulties in the incorporation of the antioxidant into the material which it is intended to protect.
U.S. Pat. No. 3,553,163 reveals alkylthio substituted mononuclear phenolic age resisters prepared by reacting an alkylthio phenol such as 2-methylthio phenol with an olefin type material such as 2-methyl-1-propene in the presence of a Friedel-Crafts type catalyst to yield compounds such as 2-tert.butyl-4-methylthio phenol.
U.S. Pat. No. 3,565,857 reveals alkylthio substituted polynuclear phenolic age resisters prepared by reacting in a one or two step process an alkylthio phenol such as 2-methylthio phenol with a condensation reactant such as an aldehyde or a ketone and subsequently reacting the product of the first reaction with a compound selected from the group consisting of olefins of 2 to 12 carbon atoms, cycloolefins containing from 5 to 9 carbon atoms and arylalkenes containing from 7 to 9 carbon atoms to produce antioxidant compounds such as 2,2'methylene bis(4-methylthio-6-tertiarybutyl phenol). U.S. Pat. No. 3,751,483 discloses phenolic thioethers wherein the sulfur atom on the phenolic nucleus is attached to an aliphatic, alicyclic or aralkyl group of 2 to 18 carbon atoms. These antioxidants are prepared by a reaction of metathesis wherein the phenolic substituents are incorporated through reaction with organic halides.
A variety of phenolic thioether compounds are known, wherein the sulfur atom on the phenolic nucleus is attached to a lower aralkyl, aliphatic or alicyclic group such as methyl, ethyl, cyclopropyl, propyl, isopropyl, benzyl or a corresponding alkenyl or alkynyl group. Such "lower" phenolic thioether compounds can be prepared, for example, by the method disclosed in U.S. Pat. No. 3,282,979 or by heating the corresponding hydroxyaryl sulfonium chlorides as taught in U.S. Pat. No. 3,133,971.
The search for new and better polymer stabilizers continues to command the attention of many skilled investigators, however, the prior art and literature on the subject does not disclose or suggest reacting polycyclic compounds containing one or more points of unsaturation or reacting monocyclic compounds containing one or more points of unsaturation with mercaptophenols. The process of the present invention and the novel compounds prepared therewith are excellent stabilizers that help overcome some of the prior art problems of stabilizer extraction, volatility and discoloration.